Containers such as bottles and packages are usually provided with labels so that consumer information can be attached. It is also known to apply markings or other information to the package using inkjet printers in order to make possible individualisations which label printing does not permit. Such printing systems work in monochrome and are restricted to few printing dots per lines.
In order to apply a polychrome print directly onto containers, a plurality of printing heads which operate in monochrome according to the inkjet principle are arranged one after the other and suitably offset so that depending on the number of the colours an always equal spacing between the individual printing dots is achieved. This is possible with an adjustment on a machine having a plurality of printing heads arranged one after the other in a defined manner. The packaging material and the printing heads in this case are moving relatively to each other with a constant speed. The output of such a machine is therefore dependent on the printing speed of a respective printing head. Although this is practicable for absorbent packaging materials, the ink, by contrast, with other materials such as metals, glass or plastic, has to be dried through heat or cured through cross-linking by means of UV or electron beams. This process has to be applied also between the printing of successive printing colours at least as so-called pinning, a “part curing”, which increases the length of such machines.
In the device described in DE 10 2008 049 241 A1 for applying a polychrome print image on a container, a plurality of modules are connected one after the other, in which different treatment steps such as pre-treatment, printing, drying and checking are carried out. The containers are transferred from one module to the next so that in each case a new positioning and adjustment is required. This impairs the accuracy of the print image and reduces the throughput speed.
From WO 2004/009360 A1 a device is known, in which the containers during printing are each arranged on a mandrel serving as container carrier. With a plurality of printing heads distributed about the mandrel, a colour image consisting of a plurality of colour sets is applied to the container while the mandrel is rotated. The mandrels are provided on a revolving driven transport element, with which the container during printing are moved on a transport section formed between a container inlet and a container outlet.
Industrial utilisation of these plants is to take place at high outputs, for example in bottle filling plants with up to 36,000 bottles per hour. Here, the bottles and thus also the printing head are transported on a rotating machine with a speed of approximately 1.5 m/s, so that the ink drops can be exposed to an airflow which can impair the print quality.
It is therefore the object of the present invention to increase the print quality during the printing of containers with high printing output and reliable function.